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idle issues


mcstein

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Lots of idle issues on this forum but can't find one similar to my experience.

88 ranger. 2.9L manual.

Just bought this truck. It ran great when I bought it. After a day or 2 it would idle rough. Almost die but it wouldn't. No check engine light. It seemed to do this intermittently. Some times I'd start it and it be fine. Other times I'd start it and I'd expect it to die at each stop light.

Now for the last couple days it dies on every start up. It won't idle. It'll start right away and then die. I can keep it going by keeping the engine rev'd but the check engine light is one. If I keep it running and start driving down the road it'll drive with the check engine light on for about 5 minutes. Then the light goes out and it runs like normal, even at idle, until I shut it off. Then it's the same story at next start whether it's right after I shut it off or hours later. It doesn't seem to matter whether the engine is hot or cold. When the check engine light is out, it runs great the rest of the time whether at speed or at idle.

To me it sounds like a sensor is on it way out. I figure if it was vacuum, it happen at every idle, and if it was fuel it happen all the time or at least every idle. Any ideas?

Tried to get a code at parts store but the reader wouldn't work. It couldn't tell it was plugged in the the truck for some reason.
 


Mike Tonon

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My mom had a 1997 Explorer 4.0 sohc that did, I think, exactly this. If I remember correctly, I think it was an IAC issue. Either carbon inside or weak electronics on it, maybe??

On the 2.9, it's on the upper PS of the upper intake. Just unplug and unbolt. Then clean it out and put it back on. If that doesn't fix it, new IAC. Should have a paper gasket between it and the upper intake. I was careful removing the IAC and reused my gasket when doing this on my 87 ranger, but probably should be changed.
 

mcstein

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I was leaning towards that. I was going to wait until I got a gasket before I pulled if off though. Is there a spring or something in there that could get stuck? Is it something I could gently tap on with a hammer to unstick it for a temp fix before I get a gasket?
 

Mike Tonon

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There's a valve in there, spring loaded. That little cylinder on the end with wires to it opens and closes it. I used to spray cleaner in there and let it sit for a while.

Tapping it might work for a while, but I don't know.
 

Primosboy

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I had this same exact issue with my old 87. I must have spent 300 bucks doin all the commonly suggested fixes. Kept getting worse until wouldn't fire up at all. I was told to connect a jumper cable from the block to the frame and try starting it. Fired right up. Ground was real bad. So that's always the first thing I check now. I know it sounds to easy but it's worth a try if you haven't already.
 

mcstein

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I had this same exact issue with my old 87. I must have spent 300 bucks doin all the commonly suggested fixes. Kept getting worse until wouldn't fire up at all. I was told to connect a jumper cable from the block to the frame and try starting it. Fired right up. Ground was real bad. So that's always the first thing I check now. I know it sounds to easy but it's worth a try if you haven't already.
That's good to know
 

mcstein

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Update on truck
now that i finally got a chance to dig in the other day

I was sure a sensor was bad because if kept tryin to start it and wiggled the wires at each one betweens starts, eventually i'd get a "good" start with out a cel and bad idle so i assumed i had a broken wire in there.

I gave it a basic tune up as an excuse to go digging around. Plugs, wires, cap rotor, fuel and air filters plus some valve cover gaskets because it needed them. I took the intake plenum off to make room and replaced those gaskets. Cleaned the iac and throttle. Both looked good.

However i found a couple spark plugs that were loose(or just barely hand tight) And all of the plugs had a wide gap. The manual says .44 but they were all at .55-.65. They looked good other then the gap. After i put it together, no more light or bad idles.

My theory is the hand tight plugs were seated just enough that when the engine warmed it would expand just enough on the plug threads to close the leak. That mixed in with the wrong gap kept it running bad. I don't know if thats's what it was but that the only thing i could find. Maybe the valve covers were leaking oil onto the plugs to affect them.

Since it idles now i could confirm no vacuum leaks and i didn't find any broken wires.

I was supprised it was fixed from just a tune up.
 
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mcstein

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While I said no more bad idle, it still has a very slight hesitation at idle once in a while. Usuall when warm. Not at start up. It's not much. It idles at 900. It may dip to 800-850 at a stop light but not everytime? Does that indicate anything to anyone?
 
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